<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .test {
            width: 0;
            height: 0;
            border: 100px solid #000;
            border-color: #000 transparent transparent transparent;
            border-radius: 50%;
        }
    </style>
</head>

<body>
    <div class="test"></div>
    <script>
        var a = 1;
        {
            let a = 2;
            {
                var a = 'xxx'
                let a = 3;
                {
                    let a = 4;
                    console.log(a)
                }
            }
        }
    </script>
</body>

</html>